Strong parallel evidence of selection during switchgrass sward establishment in hybrid and lowland ecotypes

Abstract

Background: Switchgrass sward establishment results in up to 90% seedling mortality. The degree of selection during sward establishment has not been reported using modern genetic methods. Methods: Pooled leaf samples were sequenced from replicated swards of 46 half-sib families from two breeding groups (lowland and hybrid) before and through 3 years of stand establishment. Pooled allele frequencies were then assessed using fixation indices (F st ) and an independent data set was used to predict the polygenic impact of establishment selection on two traits (heading date and winter survivorship). Last, the DNA pools were assigned survival rankings to predict the sward survival genomically estimated breeding values within the training data set. Results: Strong and parallel selection occured in both breeding groups. Five genomic regions exceeded the significant threshold of 99.9% in >10 families, indicating consistent selection across families and breeding groups. Polygenic trait predictions determined that establishment selection was partially associated with winter survivorship but resulted in variable heading date alterations. The genomewide variation is consistent with selection for a small number of related parental lines. Conclusions: This study observed strong selection for a small number of hybrid and coastal ecotype individuals which are promising germplasm sources for improved sward survival. This confirms prior reports of sward selection during grassland establishment and highlights the strength of pooled DNA sequencing for survival traits.

Switchgrass sward establishment selection is consistent across multiple environments and fertilization levels

“…The above models were solved using the R package sommer (R Core Team; Covarrubias‐Pazaran, 2016). Repeatability measures for this two‐stage analysis were previously reported by Tilhou et al (2022).…”

“…Tilhou et al (2022) found negligible variation in allele frequency response to sward survival mortality among any half‐sib families at Arlington. Therefore, this study will analyze aggregated data from all G 1 and G 2 hybrid half‐sib families at each of the three sites and in pre‐establishment samples.…”

“…A prior study of switchgrass at Arlington, WI reported strong selection pressure during sward establishment based on DNA from pooled leaf samples before and during 3 years of sward establishment (Tilhou et al, 2022). A coarse estimate of cumulative mortality based on deviations in allele frequency indicated a minimum of 90% mortality solely to selection.…”

“…This pattern of selection was also consistent across multiple field replicates and breeding populations. However, Tilhou et al (2022) only documented a single selection event in a single environment with a single management regime. Therefore, many questions remain.…”

Biomass yield improvement in switchgrass through genomic prediction of flowering time

“…Validation was also carried out on individuals from half‐sib families derived from parents selected from the training population (validation trial described above, n = 122) by predicting progeny BLUPs using GEBVs derived from the training dataset. Finally, the model was applied to a field trial of 52 half‐sib families of Gulf ( n = 20) or Hybrid ancestry ( n = 32), referred to as the SPACE study (Tilhou et al, 2022). Families in this field trial were evaluated for multiple traits, including sward yield (2.5 observations per family) for 2 years.…”